Field of the Invention
The invention relates to a safety-switch device for use on movable devices.
Discussion of Prior Art
It is known in the industry to provide a conventional safety-switch device on movable devices as a means of accident prevention. Such movable devices can, for example, be parts of larger apparatus and examples of such movable devices include freely movable articulated arms, booms, etc. The movable devices may, however, also include vehicles, such as a forklift truck. Hereinafter, reference is made to an electric motor powered forklift truck as the movable device, but it is understood that this reference is only by way of example and that it includes other types of movable devices.
It is known to provide a forklift truck with a conventional safety-switch device, whereby the switch is a switch, i.e., a flexible, deformable, strip or tube-like element, that is placed on the housing of the forklift truck. The purpose of this conventional safety-switch device is to prevent accidents and provide personal safety. With operating a forklift truck, for example, the type of accident that typically occurs is that the operator, when maneuvering the forklift truck in a tight space and, particularly, moving the truck in reverse, guides the vehicle too close to himself, so that the vehicle runs over the operator's foot. The conventional safety-switch devices are therefore placed outside on the housing of the forklift truck. This enables the fastest possible contact and, thus, the fastest possible actuation of the safety switch, which, when triggered, immediately switches off the power drive of the forklift truck. In applications on movable devices other than forklift trucks, it is possible, instead of switching the motor off, that the switch of in the safety-switch device changes or reverses the direction of travel of the device, or sets off an alarm signal.
The goal of the safety-switch device is to ensure the fastest response, i.e., the fastest triggering of an alarm of the fastest switching off of a motor, and for this reason, the safety-switch devices are placed on the outside on the movable devices in obvious places where a problem is likely to occur. This is an advantage as far as the safety response is concerned, but it does, however, increase the risk that the switch circuit itself will be damaged, for example, when coming into contact with hard objects, such a masonry walls, shelves, pallets, stationary machines, or, staying with the example of a forklift truck, when bumping into another forklift truck. If the safety-switch device is damaged, then it may become ineffective, and no longer serve its function as a safety device for the movable device. If this is the case, then the movable device is either operated in an unsafe condition or, it is taken out of operation to be repaired. In the latter case, the movable device is now unavailable and that presents an economic disadvantage.
U.S. Pat. No. 5,653,568 A1 discloses a conventional safety-switch device that can be used as a safety device on forklift trucks or on hydraulic truck loading ramps. In these circuits, the electrical contacts are placed inside a deformable hollow profile. Contact of an object against the hollow profile causes the profile to deform, i.e., the profile is compressed, so that the contacts touch each other, thereby actuating the desired switch operation. The deformable hollow profile represents in this case an integral component of the switch that bears one of the two electrical contacts. At the same time, it also provides an impact surface that has to be moved by some external pressure. Damage to this hollow profile, however, also means that the switch itself is damaged.
What is needed, therefore, is a safety-switch device that ensures the safest possible operation of a movable device. What is further needed is such a safety-switch device that has an impact surface that can be replaced quickly and without the use of tools. What is yet further needed is such a switch circuit that is easy to manufacture and easy to fit to different types of movable devices, either during production or as a retrofit.